The proposed reseach investigates the behavioral mechanisms of ethanol and diazepam. These prototyic sedative-hypnotic drugs are widely used and abused. There is a paucity of data on the effects of ethanol and diazepam on discrimation, and more specifically on duration discrimination. There is also no extant data on the relationship between discrimination difficulty and the effects of these two drugs. The proposed research will employ pigeon subjects and use discrete-trial duration discrimination methods. One group of pigeons (N=16) will be trained on a discrimination of moderate difficulty (2 vs 3 seconds); another group of pigeons will be trained on a discrimination of high difficulty (2.25 vs 2.75) seconds). The correct choice response will depend on the previously presented stimulus duration (conditional discrimination-forced choice response). After these subjects have attained asymptotic responding (based on percent correct and other dependent variables), they will be administered ethanol in doses from 0.00-1.50 g/kg. A second, naive group of 16 pigeons will receive the identical treatment just described and administered diazepam (0.00-4.00 mg/kg). Comparisons of the effects of discrimination difficulty on ethanl dose-response curves as well as comparisons on the effects of discrimination difficulty on diazepam dose-response curves will be drawn. Analysis of these data will elucidate the behavioral mechanisms of these drugs, as well as describing similarities and differences between the effects of these often used and abused drugs. It is likely that the findings will show that higher levels of difficulty will be more sensitive to both drugs. Future directions include investigating behavioral determinants of the effects of these drugs by investigating the effects of these drugs on varous behavioral tasks that can modify discrimination difficulty (by varying baseline accuracy) and investigating pharmacologic variables of importance.